1. Field of the Invention
The present invention relates to a Global System for Mobile (GSM) communications and, more specifically, to a method for detecting (or verifying) relation between a mobile radio terminal and a subscriber identity module (SIM) card in a GSM-based system.
2. Description of the Related Art
In general, a Global System for Mobile communications (hereinafter, referred to as "GSM") terminal performs a personalization function for detecting (or verifying) the relation between a mobile radio terminal and a subscriber identity module (hereinafter, referred to as "SIM") card. The personalization function is commonly called a "SIM lock" function. The SIM lock function consists of: a SIM lock verification procedure for checking whether the SIM card coincides with the mobile radio terminal into which the SIM card is inserted; and a password verification procedure for checking whether a password input by the user is identical to a password stored in the mobile radio terminal. The latter is employed when a user, possessing his or her own SIM card, utilizes another person's radio terminal. The password verification procedure allows the bill for the telephone charges to be forwarded to the person possessing the SIM card. In such a case, it is necessary to check the password, since a SIM lock code stored in the radio terminal does not coincide with a SIM lock code stored in the SIM card (thus, rendering the SIM lock verification procedure ineffective).
FIG. 1 shows a block diagram of a general GSM terminal. A central processing unit (CPU) 70 controls the overall operations of the mobile radio terminal. A memory 94 consists of an EEPROM (Electrically Erasable and Programmable Read Only Memory) for storing a program and initial service data, and a RAM (Random Access Memory) for temporarily storing data generated during operation of the mobile radio terminal. A keypad 92 generates key data for performing various functions of the mobile radio terminal including a dialing function, and provides the key data to the CPU 70. A CODEC 80, consisting of an encoder and a decoder, is connected to a speaker 82 and a microphone 84. The encoder of CODEC 80 converts an analog voice signal into a digital signal for transmission via Code Division Multiple Access (CDMA), and the decoder converts the received digital signal into the analog voice signal. A duplexer 10, connected to an antenna 12, separates a transmission Radio Frequency (RF) signal and a reception RF signal. A receiver 20 connected to duplexer 10 receives the RF signal, and a demodulator 50 detects the received signal from receiver 20 to transfer an audio signal to CODEC 80 and the received data to CPU 70. A modulator 60 modulates transmission audio signal from CODEC 80. A transmitter 30 modulates the transmission audio signal from modulator 60 and the transmission data from CPU 70, and transfers them to duplexer 10. A channel mixer 40, under the control of CPU 70, receives and transmits data for designating transmission and reception channels. The CODEC 80 communicates with CPU 70. A display 90 displays the various states of the mobile radio terminal. An IC (Integrated Circuit) card module 95, which is a data storage device in the form of a card, stores personal and system information.
FIG. 2 is a flow chart illustrating a prior art method for verifying relation between the mobile radio terminal and the SIM card. First, CPU 70 starts the SIM lock verification procedure (step 2a) if: the mobile radio terminal is powered up; the SIM card is inserted into card module 95 of the powered terminal; or the currently utilized SIM card is replaced with a new SIM card. Next, CPU 70 reads the "SIM Lock Function" setting information stored at a specified address in the EEPROM of memory 94 (step 2b).
Subsequently, CPU 70 checks whether or not the "SIM Lock Function" setting information is in an "ON" (or "SELECT") state (step 2c). If the "SIM Lock Function" setting information is in an "OFF" (or "NON-SELECT") state, CPU 70 terminates the procedure. However, if the "SIM Lock Function" setting information is in the "ON" state, CPU 70 proceeds to step 2d.
Then, CPU 70 reads the SIM lock code from the EEPROM of memory 94, and compares it with the SIM lock code stored in the SIM card inserted into IC card module 95, and checks whether or not the two SIM lock codes are identical (steps 2d and 2e). The SIM lock code is used to verify the SIM lock. If the two SIM lock codes are identical, CPU 70 terminates the verification procedure. However, if the SIM lock codes are not identical, CPU 70 proceeds to step 2f.
Next, CPU 70 compares the password input by the user with the password stored at a specified address in the EEPROM of memory 94, and checks whether or not the two passwords are identical (steps 2f and 2g). If the two passwords are identical, CPU 70 proceeds to step 2k. At step 2k, CPU 70 changes the "SIM Lock Function" setting information to the "OFF" state and then, terminates the procedure. However, if the passwords are not identical, CPU 70 proceeds to step 2h.
At step 2h, CPU 70 reads the "Residual Retry Number for SIM Lock Verification" information in the EEPROM. Then, CPU 70 checks whether or not the residual retry number is greater than zero (0) (step 2i). If the residual retry number is greater than zero, CPU 70 returns to step 2f to repeat the comparison of the passwords. However, if the residual retry number is not greater than zero, CPU 70 proceeds to step 2j. At step 2j, CPU 70 blocks the mobile radio terminal (or renders the terminal inoperable). In this manner, a fraudulent use of the mobile radio terminal by an unauthorized person is prevented.
The conventional mobile radio telephone verifies the SIM lock code and the password only when the SIM lock function is selected. Furthermore, if the "SIM Lock Function" setting information is switched from the "ON" state to the "OFF" state, the mobile radio telephone will not perform the SIM lock verification procedure even if the system is re-powered (re-started) or the SIM card is re-inserted into IC card module 95, or replaced with a new SIM card. However, it is to be appreciated that the user may require the SIM lock verification procedure to be performed at any time. Nonetheless, in the aforementioned circumstances, the conventional mobile radio telephone disadvantageously cannot perform the SIM lock verification procedure.